Video: Commercial planes face threat

It's a terrifying scenario and a big reason for the beefed-up perimeter security at Los Angeles International Airport. Al-Qaida has already targeted an Israeli passenger plane with shoulder-fired missiles, in November 2003 in Kenya. In Baghdad, a DHL cargo plane was hit and forced to turn back.

"We think it is a real and significant threat," says Rand analyst James Chow.

But Chow says outfitting each commercial aircraft in America with a missile defense system would be cost prohibitive. According to a Rand study, it would cost $11 billion to equip 6,800 aircraft and another $2 billion each year in operating costs.

By comparison, the total transportation security tab is now $4.4 billion.

"We think the expense to deploy these countermeasures at this time would not be prudent," says Chow.

That's not to dismiss the threat. Experts say thousands of shoulder-fired missiles and launchers are missing. And they remain very concerned at the Department of Homeland Security, where they're spending $122 million on an urgent push to come up with a missile defense system for commercial aircraft.

Two companies, Northrup Grumman and BAE Systems, are working on laser defense systems, competing to present proto-types to the government in 12 months.